Modern cutting machine tools perform more and more complex and tedious machining processes after a single programming. The more the human steps into the background during this provision of such processes, the more the machine tool must be able to control itself. Therefore, typically, sensors are arranged within or at the machine tool in which a data transmission as well as the energy transmission is done via cables. These cables are either directly guided to the sensors or to inductive transmission devices at immediate spatial proximity. By means of such sensors, the control of the machine tool or a controlling system connected thereto controls process conditions, for example drilling or milling of a metal, and reacts in an appropriate way on deviations with respect to a predetermined process behavior.
The integration of sensors and control modules into cutting machine tools is difficult: Many measuring points are not easy to access and comprise small sizes. However, the main difficulty is the fact that the parts to be controlled of a cutting machine tool, for example drills or milling cutters, rotate. Therefore, often a control of secondary values is performed. Instead of a measuring of the torque of a drill, for example auxiliarily the energy consumption of the driving motor is measured. Such measuring of secondary values is suitable for some use cases, however they are often inexact. A measuring possibly directly at the site of action is desirable.
From the DE 199 26 799 A1, it is known to use a distance sensor within an industrial robot or the like, which is provided with electrical energy by means of a magnetic field, which is generated by a primary coil, and which sends out radio signals about the information which is measured by the sensor. Besides the distance sensor, the DE 199 26 799 A1 comprises an exclusive list of other possible sensors which work according to this principle, namely temperature sensors, pressure measuring sensors, current measuring sensors or voltage measuring sensors. A hint on cutting machine tools and requirements in combination with the work steps of drilling and milling to a controlling sensor electronics cannot be retrieved from the DE 199 26 799 A1. This applies also for the DE 101 50 128 A1, which discloses a similar sensor system.
However, wireless sensor systems for cutting machine tools are known from the DE 44 32 808 A1 and the DE 101 63 734 A1. The DE 44 32 808 A1 discloses a system which is capable of transmitting sensor signals of a sensor which is directly connected to the secondary coil of a transformer-like arrangement, via transformer like coupling. Thereby, secondary voltages arise, which are generated out of the measured signal without preprocessing and which can be measured on the primary side. This system allows the use of sensors at not easily accessible or rotating elements of cutting machine tools, for example the shaft of a drill or a milling cutter. It, however, does not provide a solution for sensor electronics which are not directly connectible to an inductive transmission link. This includes particularly the nowadays common strain gauges by which normal forces and torques at shafts of a cutting machine tool are measured.
The DE 101 63 734 A1 describes a system in which the sensors of a cutting machine tool are exposed to a magnetic alternating field to generate the required operation energy. The energy generation functions according to the transformer principle. The energy-generating coil thereby forms the primary coil and the coil of the sensor electronics provides the secondary coil. The transmission of the data measured by the sensors at the machine tool happens by means of load modulation of the introduced magnetic alternating field by the sensor electronics. At an appropriate orientation of the primary and the secondary coil, the induction effect and the signal transmission is not influenced by a rotation of the area to be measured, such that this method is particularly useful for the control of cutting machine tools. Since only one single secondary coil is needed within the machine tool, the disclosed system can be realized particularly space-saving and it can therefore be integrated into the area of the small receptacles for the common tools of a cutting machine tool, for example a single drill or a milling cutter.
However, this method in practice comprises a series of disadvantages:
As a frequency of the magnetic alternating field, which simultaneously transmits the energy for the sensor electronics and the data, in general the range up to 125 kHz is used. This frequency range is purposeful for the effective energy transmitting since in the proximity of metals, magnetic alternating fields are attenuated by circular fields and this effect increases at higher frequencies. To transmit as much energy as possible, it is therefore common to stay in the range up to 125 kHz. The data transmission rate of a transmission link depends mainly on the frequency of the carrier wave and can be in every case only a fraction of it. The method according to the DE 101 63 734 A1 therefore leads to data rates of approximately 4 kBaud at carrier waves of 125 kHz. Therefore, the information provided by the sensor electronics is heavily limited in its extent as well as in its actuality.
Further, the transmission of data from the sensor electronics to the energy-consuming unit decreases the energy which the sensor can generate from the field which surrounds the sensor, since its field strength must be varied by principle. As a result, either the data or the energy amount is thereby limited which can be transmitted from respectively to the sensor electronics.
If more sensor electronics' are provided at a cutting machine tool, they have to share the maximum usable data rate. Therefore, the already limited data rate further decreases.
Finally, systems, which use an inductive energy transmitting, must introduce high energy amounts into the primary coil due to dispersion effects, particularly if high distances of energy transmitting are needed, for example due to construction reasons. The higher the energy amounts are, the more difficult it will be to extract the load modulation from a sensor from its input signal. Therefore, as a result, at the systems according to the DE 101 63 734 A1 only limited distances can be achieved.
It is therefore the problem of the present invention to provide a sensor system for a cutting machine tool which overcomes the above-mentioned disadvantages of the prior art and particularly allows higher data rates for the transmission of the values received by the sensor systems and allows large distances and thereby considers the peculiarities and requirements of a cutting machine tool.